Diffraction Grating Polarization Sensitivity Reduction
Solution Overview
Problem
Current augmented and virtual reality display systems face challenges in providing a comfortable and natural presentation of virtual image elements amidst real-world imagery due to polarization sensitivity issues in diffraction gratings, leading to inefficient light coupling and reduced image quality.
Innovation Solution
A head-mounted display system incorporating a waveguide with a diffraction grating having a first diffraction efficiency for one polarization and a second diffraction efficiency for another polarization, where the first efficiency is 1 to 2 times the second efficiency, achieved by using a substrate with a high refractive index and a multilayer coating to reduce polarization sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional diffraction grating is used in the waveguide, then light coupling efficiency is improved for one polarization, but polarization sensitivity increases causing image quality degradation
Solution Approach 1:
The patent modifies the physical parameters of the diffraction grating by adjusting the groove depth, groove width, and period spacing to optimize diffraction efficiency while reducing polarization sensitivity. By changing these geometric parameters, the system achieves improved light coupling for both polarizations without significant image quality degradation.
Solution Approach 2:
The patent employs a composite structure combining the waveguide substrate with an integrated diffraction grating pattern. This composite design allows the grating to be formed as part of the waveguide itself or as a closely integrated component, enabling optimized light coupling while maintaining polarization balance through careful material and structural design.
2Illumination intensity
If diffraction grating efficiency is increased for one polarization, then brightness is improved, but polarization-dependent artifacts increase
Solution Approach 1:
The patent adjusts the diffraction grating parameters including groove depth, width, and period to balance the diffraction efficiency for both polarizations. By optimizing these parameters, the system achieves sufficient brightness while minimizing the polarization-dependent artifacts that would otherwise degrade image quality.
Solution Approach 2:
The patent applies different local characteristics to different regions or aspects of the diffraction grating structure. By varying the groove geometry locally or using different grating regions for different functions, the system optimizes brightness in certain areas while suppressing polarization artifacts in others.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances the field of view and brightness of virtual/augmented/mixed reality displays by improving light incoupling and outcoupling efficiencies, reducing polarization-dependent artifacts, and providing a more immersive user experience.
Implementation Method 1
The waveguide can include a substrate configured to guide at least a portion of the light from said light projection system coupled into the waveguide
Implementation Method 2
The diffraction grating can include material different than said substrate over said substrate. The diffraction grating can have a first diffraction efficiency for a first polarization over a range of angles of light incident thereon
Data Source
AI summary
Diffraction gratings provide optical elements, e.g., in a head-mountable display system, that can affect light, for example by incoupling light into a waveguide, outcoupling light out of a waveguide, and/or multiplying light propagating in a waveguide. The diffraction gratings may be configured to have reduced polarization sensitivity such that light of different polarization states, or polarized and unpolarized light, is incoupled, outcoupled, multiplied, or otherwise affected with a similar level of efficiency. The reduced polarization sensitivity may be achieved through provision of a transmissive layer and a metallic layer on one or more gratings. A diffraction grating may comprise a blazed grating or other suitable configuration.